Axial-piston machines of the aforedescribed type are known in the art and can be used as hydrostatic motors or hydrostatic pumps, most often as variable-displacement pumps, the displacement being a function of the degree of tilt of the inclined disk (swash plate) or control surface. When in operation, the cylinder drum of the pump is rotated about its axis, e.g., by a shaft journaled in the housing, which can have a prismatic configuration, e.g., a square or rectangular cross section, so that the pistons of the drum are caused to move inwardly and outwardly as they orbit against the inclined plane. Means is customarily provided to displace the control surface about its pivot axis.
In German open specification (Offenlegungsschrift) DT-OS No. 2,240,579, the control surface is formed as a flat face of a rocker which can be tilted about an axis parallel to the plane of the surface by a setting piston. In this construction, a setting cylinder is provided to either side of the pivot axis and the two setting cylinders lie in a common plane perpendicular to the pivot axis of the rocker, the setting pistons acting upon projections from the rocker.
This construction in which the longitudinal median plane through the cylinder drum coincides with the plane of the setting cylinders, requires considerable space and increases the dimensions of the machine to accommodate the setting cylinders over the size which would be required simply to house the drum and rockers absent these cylinders. As a consequence, the machine is heavy and the cost of fabrication, in terms of additional material and the like, is high.
It has also been proposed (see U.S. Pat. No. 3,779,137), to provide an axial-piston machine in which the setting cylinders can have their axes parallel to the axis of rotation of the setting drum. Another arrangement has the disadvantage that an articulated linkage is required between the piston of the setting cylinder and the rocker. Once again, the housing must be enlarged over the minimum prismatic housing accommodating the drum, to receive the actuating cylinders, their pistons and the respective linkages, if any.